To date, the character that has been the most difficult for Marvel to figure out on film has been the Incredible Hulk. He was put on the big screen in a film directed by Ang Lee. Then, the character was rebooted by Edward Norton, and eventually recast in the first Avengers film. Today, following two Avengers movies, and with plans for the Hulk to return in more, it’s clear that they have finally figured out what the character needed. Mark Ruffalo, the actor who now plays the part, credits director Joss Whedon with figuring it all out, which is why he’s still a little upset that Whedon won’t be back for more.

Because Joss Whedon directed the first Avengers movie he was the one who actually cast Mark Ruffalo as the new Bruce Banner of the MCU. It’s something of an odd situation for Ruffalo, since now Whedon has left the series, yet Ruffalo continues on, making more movies in the series. He has all the faith in the world in the Russo Brothers, who will be directing both parts of upcoming Infinity War story, but he tells Yahoo that he does miss working with Joss, and explains why:

He basically told me [he was leaving], and I was like ‘Goddamn it, you dragged me in to this world and now you’re abandoning me here!’ But they’re doing fine. Joss’ll do fine. I just miss him, and I will miss him. He cracked this character, he obviously cracked the Avengers which was nearly impossible. It was a miracle and he did it so beautifully. I think the Russo brothers are great and I think they’re well positioned to take it on, and I’m happy to be doing it with them, but I’m friends with Joss. He had a hard time making the first one and he had a hard time making this one. I think it’s partially the nature of that beast.

Joss Whedon has made no secret of the fact that making the Avengers movies for Marvel, especially Age of Ultron, was an incredibly difficult process. While he has said the main reason he left was simply so that he could do different things, it’s also clear that he simply needed to take a break from the MCU. The first Avengers was a movie that nobody was entirely sure would even work. The film was going to prove the success or failure of the MCU experiment, so quite a lot was riding on the film's shoulders. Add to that the fact that the movie had to try and figure out how to use the Hulk properly, because nobody had yet, and it’s easy to see why it was all so difficult.

Mark Ruffalo’s feelings are completely understandable. While all the other members of the MCU had made at least one movie before the big team up, he was brought in by Joss Whedon. For him, the experience of making a Hulk movie, and working with Whedon, are the exact same thing. Add to that the fact that the two are real friends and you can see how the idea of playing the Hulk without him could feel very different.

The Russo Brothers did a fantastic job with Captain America: The Winter Soldier, so we have pretty strong confidence that they’ll be able to pull their Marvel movies off. Still, it will be quite a feat, as they have even more characters to juggle in Civil War than Joss Whedon did.